A nonlinear or bistable optical device having a very low switching energy is described in U.S. Pat. No. 4,546,244, issued to David A. B. Miller on Oct. 8, 1985. This device has a semiconductor quantum well region which is electrically controlled to change its optical absorption and, in turn, the optical state of the device. The device is operated with one or more input light beams. However, a problem of this device is that it has only one output light beam. As a consequence, the device has limited system applications where complementary output light beams are required.
In one configuration where the device is operated with two input light beams, the power of one of the input light beams is maintained at a constant level, and the power of the other light beam is varied to change the optical absorption and the state of the device. A problem with this configuration of the device is that removal of either input beam before the other causes the device to lose its present state.
Another problem with this configuration of the bistable optical device is that once the power level of the constant power level light beam is established, the power range of the variable light beam applied to the device for causing the device to change from one state to another is fixed.